Sometimes chasing a rumor is instructive, even if the story you thought you had doesn't pan out.

Some years back, Ron helped unearth a rogue running bamboo growing under a hillside house and brought the brutally ripped-out plant home. It prospered as a houseplant for years. Running bamboo is tough to squelch, tough to catch and can take off and turn up yards away if you turn your back on it - very like a rumor.

A friend told us recently that his neighbor had said her black bamboo (Phyllostachys nigra) was dying. Given what we knew about gregarious flowering in bamboos - a particular species of bamboo blooms over a wide area, then dies off - it seemed worth pursuing.

None of the nurseries we called had anything happening with their black bamboo, but all had experienced bloom-and-bust cycles with other bamboo species.

"In the 1980s, there was a widespread flowering of Mexican weeping bamboo (Otatea acuminata ssp. aztecorum), an important ornamental," John Ballantine of Berkeley Horticultural Nursery recalled. "It all flowered and died and had to be started from seed." Scott Hunter of Bamboo Giant in Aptos reported that some - but not all - of his nursery's dwarf white-stripe bamboo (Pleioblastus fortunei) is flowering now.

Jesus Mora, the grower at Sebastopol's Bamboo Sourcery for 20 years, said that in the past couple of years, some of his dwarf ground-cover bamboos, including the dwarf white-stripe, have started to flower. Mora says he has seen at least 20 bamboo varieties flower: fountain bamboo (Fargesia nitida) 11 years ago, umbrella bamboo (F. murielae) seven years ago, golden groove bamboo (Phyllostachys aureosulcata 'Spectabilis') last spring.

Gregarious flowering has serious consequences for wildlife and humans alike: At least 138 giant pandas perished when bamboos in the genus fargesia, a major food source, died off from 1974 to 1976. In the past, pandas could shift to other bamboos with different cycles; habitat loss has made that harder. A bamboo species introduced to Thailand for its edible shoots flowered and died all over the country in 1994. The resulting crash in bamboo-shoot exports was an economic disaster.

In India, where 70 of the 72 native species undergo gregarious flowering, the association between bamboo flowering and famine dates at least back to the Mahabharata, composed more than 2,000 years ago. Northeast India in particular is subject to outbreaks of rats when the bamboos bloom and set seed. Feasting on the seeds, the rat population explodes. In the northeastern state of Mizoram, 2.5 million rats were killed during a bamboo bloom in the 1970s. When the seeds are gone, the rats descend on villages and attack standing crops and grain stores. Last year the bamboo flowered again in Mizoram, and this spring the rats came back.

South Americans have recorded rodent outbreaks - ratadas - linked with bamboo flowering since the 16th century.

Why have bamboos evolved this odd way of reproducing? Some theories have invoked climatic factors, even sunspots. Tropical ecologist Daniel Janzen suggested in 1976 that bamboos flower en masse to frustrate seed predators - the predator satiation hypothesis. For short periods at long intervals, the plants flood the market. Rodents and other predators can't devour all the seeds. The long cycles prevent predators from tracking the glut of seeds as a predictable resource. Janzen compared gregarious flowering to the mass emergence of cicadas on a 13- or 17-year cycle.

But that notion has been questioned. Other plants, like oaks, go in for mass synchronous seed production but don't die afterward. And the centurylong cycles of some bamboos are far longer than needed to outlast short-lived seed predators. Jon Keeley of the National Science Foundation and William Bond of the University of Cape Town in South Africa proposed an alternative theory in 1999.

They believed fire was the key. Bamboos, they argued, grow in open patches in forests. Mass die-offs create a fuel load for intense fires that prevent trees from closing gaps in the forest canopy. The bamboos thus create the disturbances needed for optimum growth.

(It's perhaps an effect of human life - and attention spans - that we compress such cycles into nearly invisible metaphors, talking about whole species as if they were somehow acting with will and strategy. Hard to avoid, dangerous to take literally.)

Other scholars, like Ted Meredith, aren't willing to credit any theory yet. Meredith mentions chemical stress, drought and the plants' accumulation of enough vigor and mass to blow it all in the expensive flowering process. Maybe it's more like salmon's than cicadas' lives.

Gregarious flowering in the wild is less predictable and less instantaneous than TV nature shows might leave you believing. It may take years, and often doesn't involve a whole species, let alone whole forests that often mix many species. The widespread, fast flowering we see in gardens might be a result of the fact that bamboos are typically - of necessity - propagated by cloning, and a clone will more likely bear the effects of whatever causes flowering all at the same time.